1. Field
The presently disclosed subject matter relates to an optical deflector apparatus. The optical deflector apparatus can be applied as an optical scanner to a laser pico projector, a laser radar, a bar code reader, an area sensor, an adaptive front-lighting system (AFS) type head lamp, a head-up display unit, and other optical apparatuses, to generate scanning light.
2. Description of the Related Art
Generally, in an optical scanner or the like, an optical deflector apparatus is constructed by a micro electro mechanical system (MEMS) device manufactured by using semiconductor manufacturing processes and micro machine technology.
A prior art optical deflector apparatus as a MEMS device is constructed by a mirror, an outer frame (fixed frame) surrounding the mirror, piezoelectric actuators coupled between the mirror and the outer frame, serving as cantilevers for rocking the mirror with respect to an axis (X-axis) of the mirror in a rocking operation mode (see: JP2012-198314A).
On the other hand, in an AFS control, when a steering angle read from a steering angle sensor or the like is larger than a predetermined value, the area of high luminous intensities needs to be shifted from a central position of the head lamp to a right side or a left side of the head lamp, to substantially decline the optical axis of the head lamp while the visibility in a high-beam mode is maintained. If such an AFC control is applied to the above-described prior art optical deflector apparatus, an offset voltage is applied to the piezoelectric actuators to deflect the mirror around the X-axis. This is called an offset operation mode.
In the above-described prior art optical deflector apparatus, when a rocking operation mode and an offset operation are simultaneously carried out, rocking drive voltages are offset by an offset voltage corresponding to the shifted amount of the optical axis of the head lamp, for example. In other words, the offset voltage is combined with the rocking drive voltages to generate combined drive voltages which are applied to the piezoelectric actuators (see: FIGS. 14, 15, 16 and 17 of JP2012-198314A). In this case, the piezoelectric actuators are used commonly for a rocking operation mode and an offset operation mode.
In the above-described prior art optical deflector apparatus, however, when the combined drive voltages become larger than a threshold value corresponding to the maximum rocking angle of the mirror with respect to the X-axis of the mirror, the piezoelectric actuators would be damaged. Therefore, the offset voltage is limited, so that the combined drive voltages do not exceed the threshold value. As a result, the offset deflecting amount of the mirror cannot be increased. Otherwise, if the offset voltage is caused to be increased, the rocking drive voltages need to be decreased. In this case, it is impossible to increase the rocking amount of the mirror.